Workpieces, in particular sheets, may be processed with accuracy by laser processing methods, in particular laser cutting and laser welding. Depending on the processing methods and on the workpiece to be processed, laser processing requires different laser beam diameters at the workpiece in order to optimize the speed of the laser processing and the processing quality. Laser cutting of different material strengths of the workpiece can require different laser beam diameters.
In a laser processing machine including a solid-state laser, the laser beam is guided to a laser processing head by means of an optical fiber. In the laser processing head, the laser beam emerging in a substantially divergent manner from an end of the optical fiber is usually collimated first by way of a collimating lens (or lens group). The collimated laser beam is subsequently focused onto the workpiece to be processed by a convex lens (or lens group). In such a laser processing head, switching between two laser beam diameters can include interchanging the collimating lens (or lens group) or the convex lens (or lens group).
DE 102 15 446 A1 describes a combined laser head for different types of laser processing. In one embodiment, the ends of an approximately z-shaped shaft have a lens arranged at one end and a lens-nozzle module arranged at the other end. The shaft is rotatable about the axis of the middle piece. Furthermore, the shaft may be swiveled about a swivel axis extending perpendicular to the laser beam by means of a swiveling device. The swivel axis can extend perpendicular to the axis of the middle piece. The lens and the lens-nozzle module may be alternately swiveled into the beam path of the laser beam. In another embodiment, a plurality of attachment devices, each with a positive lens, are arranged in a revolver disk. The revolver disk is rotatable about an axis which extends inclined by 45° in relation to the laser beam.
DE 196 30 147 C2 has disclosed a connection head for processing a workpiece by means of a laser beam. In one embodiment, the carriers, which each have a plurality of receptacles for focusing optical units, are rotatable about an axis extending parallel to the laser beam.
The interchange mechanisms can require much installation space on the laser processing head and, in part, have a relatively complex structure.
Furthermore, WO 2011/131541 A1 has disclosed a beam-forming unit for focusing a laser beam, in which the beam diameter is adjustable in a completely variable manner by means of a zoom lens. This beam-forming unit has a particularly complicated structure.